In remarking on disorders of fluency, it is rather interesting that stuttering occurs in 10-45% of all individuals with Down syndrome, as opposed to only a 1% occurrence in the general population (Guitar, 1998), and that cluttering is even more common. Cluttering is also a fluency disorder. It is characterized by rapid or irregular speech patterns, and sounds jerky or has pauses that can be too short, too long, or improperly placed. In a study following 76 subjects with Down syndrome, Van Borsel and Vandermuelen (2008) discovered an occurrence of cluttering in 78.9%, and 17.1% of subjects who both stuttered and cluttered.
Guitar, B. (1998). Stuttering: An integrated approach to its nature and treatment. Philadelphia, PA: Lippincott Williams & Wilkins.
Van Borsel, J. & Vandermeulen, A. (2008). Cluttering in Down syndrome. Folia Phoniatrica et Logopaedica, 60(6), 312-317.